For the development and manufacturing of semiconductor substrates, it is necessary to carry out various tests and assessments during the different stages of production specifically for semiconductor substrates that are part of a wafer. As is known, the probe stations which basically comprise a chuck with a support surface which supports the devices under test (DUT) on the semiconductor substrates to be measured, are used for those tests. The chuck is mostly movable in x- and y-directions. Further, the probe station has a probe support with sensors, also called probes, to electrically contact the devices under test (DUT). For producing the electrical contacts, a relative movement in z-direction between the probes and the devices under test is necessary besides the movability in the x-y plane, which is consistently defined as the plane in which the support surface of the chuck is located. The required movements in z-direction are mostly realizable in connection with a positioning device of the probe support.
Because small leakage currents within the mentioned measurement range already lead to a distortion of measurement results, a probe station has a shielding system through which the electromagnetic interference can be minimised. With conventional probe stations, the EMI shielding system is made of a housing of electrically conductive materials in which at least the chuck or other devices for supporting the semiconductor substrates, including their positioning device as well as devices for incorporating and positioning of the probes are arranged, and therefore are shielded from electromagnetic and optical interferences. The external interfaces of the shielding are the cables of the measurement instruments that comprise the devices to control and analyse measurements.
Often in addition to the housing, a triaxial formation of the measurement instruments is realized. At the same time, two shields which consist of electrically conductive material are arranged opposite, i.e. adjacent to the support surface of the chuck. The outer components, e.g. the wall of the housing, serves for EMI-shielding and the element in the middle, e.g. the inside encasing or shield, serves as a so called guard. The guard is kept at the same potential as the DUT, so that even a very low, measurement results distorting, leakage current is avoided between those two elements (See DE 19638816 A1).
The chuck also has such a triaxial formation. In this case, the support surface of the chuck on which the substrate lies and which is at least electrically conductive in some sections, is kept at a force-potential. The guard which is separated from the support surface by an insulating layer extends underneath the support surface. The shield—also electrically insulated from the guard—is underneath the guard. The support surface, the guard and the shield can be realized in form of differently conductive layering with insulating layers lying in-between, whereas the shield is connected to ground, mostly to the housing or is carried out floating, and the guard is kept at a potential that is at least nearly consistent with the force-potential but decoupled from it. In this way, the wafer is efficiently shielded from interfering sources that are in the proximate surrounding of the wafer such as the drives of the positioning device of the chuck.
Also, components of the signal transmission can be included in the shielding system. The signal preprocessing devices which prepare the measurement signals from the probes for the transmission are arranged within the housing in separate chambers which again are electrically shielded from the devices under test through their walls (See DE 102007053862 A1).
For measuring the devices under test, a defined arrangement of probes, mostly consistent with the density and the size of the contact pads to be contacted of the device under test as well as consistent with probes adjusted to the measurement signal, is placed on several contact pads at the same time and through the probes electrically connected to measurement devices for measuring the properties of the device under test. By means of the probes, the device under test can be supplied with a signal, or a signal can be picked up from a device under test.
As devices under test, various semiconductor substrates are suitable which are often still on the wafer. With such on-wafer-measurements, the rear side of the wafer that rests on the chuck is often connected as well to receive the signals from rear sided electrical contacts, or to feed them into those, or the rear side of the wafer is energized by a defined potential during the measurement. That takes place via the support surface of the chuck by electrically connecting the entire surface or certain contact areas with the measurement device.